Microcalcifications as elastic scatterers under ultrasound

Abstract

One of the fundamental limitations of medical ultrasound in the imaging of the breast is the inability of current practice to reliably visualize microcalcifications in the size range of clinical interest. Microcalcifications (MCs) are small crystals of calcium phosphates that form in human tissue through a number of mechanisms. The size, morphology, and distribution of MCs are important indicators in the mammographic screening for and diagnosis of various carcinomas in the breast. The authors are investigating the imaging of MCs under ultrasound in the interest of extending the utility of medical ultrasound in the breast clinic. They present an analysis of the acoustic properties of MCs modeled as elastic spheres based on the Faran model that considers the predicted complex spectra and spatial coherence of echoes from MCs. They have found the predictions of the model to be similar to ultrasound echoes from suspected MCs in vivo. They also present breast phase aberration estimates and spatial and frequency compounding results based on the echoes from these targets.

Broadband amplitude and phase sonar calibration using LFM pulses for high-resolution study of hard and soft acoustic targets

“…For elastic targets this explanation becomes complicated due to resonances. An analogy has been drawn to spatial coherence/incoherence [28], and to distributions of the apparent position in loudspeaker response [29]. This can impact detectability, as targets depart from a point scatterer.…”

Angular scatter ultrasound imaging of wavelength scale targets

“…Calcifications with diameters on the order of one wavelength are an example of elastic scatterers relevant to medical imaging that have been modeled using the Faran theory. 10,11 Calcified lesions will generally have more complicated geometries than the monofilaments, so conclusions drawn from the monofilament data may not be directly applicable to angular scatter detection of calcifications.…”

The direct estimation of sound speed using pulse–echo ultrasound

“…We consider the 20-ns rms case to represent mild aberration, and it is on the order of phase errors that we have observed in echoes from shallow targets in the breast. 41 The 50-ns rms case represents aberration on the order of that observed in through-transmission measurements in both the breast 36 and breast tissue specimens. 39 These results are presented for a point target, such that the aberration is reflected only as a phase error on receive and has no impact on the spatial coherence of the target's echoes.…”

“…[31][32][33][34][35][36][37][38][39][40][41] Currently there is no consensus on how these types of errors can be realistically modeled. In the simple analysis presented here, we draw a distinction between two components of aberration.…”